在 Realm 和 SwiftUI 中使用 @ObservedResults 时如何完全删除项目

Question

我正在使用Realm 文档Integration Guides -> SwiftUI & Combine 中给出的示例尝试新的Realm 10 包装器，我喜欢使用@ObservedResults 和@ObservedRealmObject 时添加和删除记录是多么简单.我不太明白的一件事是为什么在从Group 对象中删除项目时，它只会从Group 中删除项目，但不会删除Item 领域对象中的实际项目。请参阅下面的领域浏览器图像。

这是通过应用程序 UI 添加和删除四 (4) 个项目后 Realm Browser 显示的内容，您可以看到这四 (4) 个项目已从 Group 中删除，但所有四 (4) 个项目都保留在Item 对象。

有人可以解释为什么在调用.onDelete(perform: $group.items.remove) 时，项目不会从Item 对象中删除，而只是从Group 对象中删除？我怎样才能删除它们？

我试着像这样删除它们...

ItemsView.swift

.onDelete(perform: deleteItems)


func deleteItems(at offsets: IndexSet){
    let realm = try? Realm()
    
    try! realm?.write {
        // 1. delete items
        for item in list.items{
            realm?.delete(item)
        }
        // 2. delete the list
        realm?.delete(list)
    }
}

但我收到以下错误：

线程 1：“只能从它所属的 Realm 中删除一个对象。”

同样，整个代码可以在Integration Guides - 不同步。

编辑：为 LocalOnlyContentView、ItemsView、Group 和 Item 模型添加了代码。

Item.swift

    import Foundation
    import RealmSwift

    /// Random adjectives for more interesting demo item names
    let randomAdjectives = [
        "fluffy", "classy", "bumpy", "bizarre", "wiggly", "quick", "sudden",
        "acoustic", "smiling", "dispensable", "foreign", "shaky", "purple", "keen",
        "aberrant", "disastrous", "vague", "squealing", "ad hoc", "sweet"
    ]
    /// Random noun for more interesting demo item names
    let randomNouns = [
        "floor", "monitor", "hair tie", "puddle", "hair brush", "bread",
        "cinder block", "glass", "ring", "twister", "coasters", "fridge",
        "toe ring", "bracelet", "cabinet", "nail file", "plate", "lace",
        "cork", "mouse pad"
    ]

    final class Item: Object, ObjectKeyIdentifiable {
        @Persisted(primaryKey: true) var _id: ObjectId
        @Persisted var name = "\(randomAdjectives.randomElement()!) \(randomNouns.randomElement()!)"
        @Persisted var isFavorite = false
        @Persisted(originProperty: "items") var group: LinkingObjects<Group>
    }

Group.swift

import Foundation
import RealmSwift


final class Group: Object, ObjectKeyIdentifiable {
    @Persisted(primaryKey: true) var _id: ObjectId
    @Persisted var items = RealmSwift.List<Item>()
}

ItemsView.swift

struct ItemsView: View {
    @ObservedRealmObject var group: Group

    var leadingBarButton: AnyView?
    
    var body: some View {
        NavigationView {
            VStack {
                // The list shows the items in the realm.
                List {
                    ForEach(group.items) { item in
                        ItemRow(item: item)
                    }
                    .onDelete(perform: $group.items.remove)
                    .onMove(perform: $group.items.move)
                }.listStyle(GroupedListStyle())
                    .navigationBarTitle("Items", displayMode: .large)
                    .navigationBarBackButtonHidden(true)
                    .navigationBarItems(
                        leading: self.leadingBarButton,
                        trailing: EditButton())
                HStack {
                    Spacer()
                    Button(action: {
                        $group.items.append(Item())
                    }) { Image(systemName: "plus") }
                }.padding()
            }
        }
    }
}

LocalOnlyContentView.swift

struct LocalOnlyContentView: View {
    @ObservedResults(Group.self) var groups
    
    var body: some View {
        if let group = groups.first {
            AnyView(ItemsView(group: group))
        } else {
            AnyView(ProgressView().onAppear {
                $groups.append(Group())
            })
        }
    }
}

SceneDelegate.swift

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    let contentView = LocalOnlyContentView()
    
    if let windowScene = scene as? UIWindowScene {
        let window = UIWindow(windowScene: windowScene)
        window.rootViewController = UIHostingController(rootView: contentView)
        self.window = window
        window.makeKeyAndVisible()
    }
}

Answer 1

请记住，该教程中显示的是如何从组的列表中删除一个项目，而不是如何完全删除该项目。

这个答案的水平很高 - List 中的对象不是实际的对象 - 它们是指向存储在磁盘上的实际项目的“指针”。

假设你有三个项目

Item 0 
Item 1
Item 2

和一个包含项目列表的组

MyGroup
   List of items
        Item 0
        Item 1
        Item 2

实际发生的事情是列表“指向”磁盘上的项目

My Group
   List of items
      pointer to Item 0
      pointer to Item 1
      pointer to Item 2

所以当它被称为$group.items.remove 时，它会从列表中删除指向该项的指针，而不是该项本身。

解决方案（嗯，解决方案之一）是删除实际项目

let myItemToRemove = List of items[0] //get the item at index 0

realm.remove(myItemToRemove) // removes the item itself from realm, along 
                             //    with the pointer stored in the list

实际删除项目的代码是这样的

try? realm.write {
   realm.delete(objectToDelete)
}